The present invention relates to packaging of semiconductor integrated circuits. More particularly, the invention provides a device and method including a die having a laterally conducting structure and a ground contact coupled to a certain lead frame having a novel lead configuration. Merely by way of example, the invention has been applied to power IC chips, but there may be many other applications.
In recent years, the evolution of semiconductor packaging technology, semiconductor technology, and consumer product applications have converged and led to a series of innovations influencing each other to improve the end product. This convergence began about ten years ago when metal oxide semiconductor field effect transistor (MOSFET) technology allowed for the creation of semiconductor chips or dies exhibiting sufficiently low resistance to allow them to perform useful work when mounted on ordinary personal computer (PC) boards, rather than on specialized heatsink structures. Applications ushering in this evolution away from the use of heatsinks included early hard disk drives and portable, battery powered electronic products, with whom the bulk and power consumption associated with conventional heat sinks precluded their use.
Positioning power MOSFET chips (i.e. chips having outputs that can conduct from 1 to 20 Amps, with “on” state resistances ranging from 10 mOhm to as much as 1 Ohm) in contact with a PC board rather than a heatsink represented a departure from prior concerns about heat dissipation, such that package designers were confident that new devices would exhibit sufficiently low resistance to handle the applied current, without generating more heat than could be effectively dissipated by an ordinary PC board. Once power MOSFET switches avoiding the use of heatsinks were mounted and used like other components mounted on the PC board, their packages were adapted from ones already being used for integrated circuits (ICs). The ability of these existing IC packages (such as the JEDEC registered SO, and TSSOP series) to dissipate heat from power MOSFET switches was enhanced utilizing techniques such as 1) tying together multiple pins or contacts, 2) tying pins directly to the die, and 3) fabricating lead frames from copper material exhibiting superior heat conductance. In this manner, balance was achieved between the ability of a power MOSFET package to transfer heat to the PC board, and the ability of the PC board to in turn dissipate heat received from the package.
The continued development of MOSFET and IC technology has allowed simple power MOSFET devices to evolve into power integrated circuit (PIC) devices having dies and packages of approximately the same size as power MOSFET devices. At the same time, the ever-increasing demand for products conforming to tight space requirements and high power demands (such as cell phones and portable imaging and computing products) has rendered such PIC devices highly desirable for use in any number of potential applications.
Therefore, there is a need in the art for new and improved packages for PIC devices which improve the efficient use of space, allowing a die of a maximum size to be contained within as small a package as possible.